1. Field of the Invention
The present invention relates generally to media players, and more specifically to recording and playback tracking control on a media player.
2. Background of the Invention
Media players include devices commonly referred to as Compact Disc (CD) players, Digital Video Disc (DVD) players, Video Laser Disc (LD) players, and others. Media players typically operate by embedding data into a disc and/or reading the data from the disc with a laser beam. The disc usually spins and an optical pickup that houses the laser is moved in a radial direction about the spinning disc allowing the laser beam to be positioned above any area on the disc where information needs to be read from or recorded to.
It is desirable for more information to be embedded onto the disc because more information allows the user to watch a longer movie, listen to more songs, or make use of more functionality on the same type of disc. More information can be embedded into the disc by packing the information more closely together and rotating the disc faster while moving the optical pickup more precisely. This creates problems because the disc has a relatively large mass, so to spin it at a very high speed while still steadying the disc enough to be read by the laser is very difficult. Moreover, to move the pickup radially with precision is difficult as well. Before further discussing this problem, an overview of media players is provided.
Media Players
An optical media player can be either a device or system that is capable of retrieving information stored in an optically recordable medium, such as an optical disc, or a device or system that is capable of both recording information to and retrieving information from an aptically recordable medium. Examples of devices that are capable of retrieving information from an optical disc include CD players, LD players, DVD players, and compact disc read-only-memory (CD-Rom) drives. Examples of devices that are capable of both recording information to an optical disc and retrieving information from an optical disc include recordable mini-disc (MD) players, magneto-optical (MO) disc drives and compact disc recordable (CD-R) drives.
Information is generally stored by an optical disc in the form of concentric or spiral tracks sometimes referred to as information tracks. In the case where information is already stored by an optical disc, the information tracks contain regions of optical contrast that represent the stored information. In the case of an unrecorded or blank optical disc containing pre-formatted tracks for recording information, a track that will become an information track may or may not have regions of optical contrast. The area located between two information tracks on an optical disc is sometimes referred to as a non-information track.
When an optical storage device is in its normal mode of operation, (i.e. retrieving information from or recording information to an optical disc), the storage device rotates the disc while using a light beam to retrieve information from or record information to the disc. As the optical disc rotates, the light beam radially traverses the disc. While the light beam traverses the optical disc, a tracking servo loop in the optical disc storage device keeps the beam of light centered on the information track, or the track that will become the information track in the case of recording information to a disc.
Tracking Servo
An optical disc tracking servo is a closed loop system that allows a light beam to remain centered on an optical disc information track during normal operation of an optical disc storage device. The tracking servo readjusts the radial position of the light beam by sensing when the light beam drifts off the center of the information track. The tracking servo senses when the light beam is not centered on an information track by measuring the intensity of light reflected by the surface of the optical disc.
Generally, the intensity of light reflected by the surface of an optical disc is the least when it is reflected by the center of an information track. Using this principle, a tracking servo generally senses the intensity of light reflected at one or both edges of an information track to detect when a light beam is drifting off center and to determine in which direction the light beam is drifting. Therefore, a tracking servo system that is in a closed loop mode of operation senses when the light beam floats off the center of the information track by detecting changes in the intensity of light reflected at one or both edges of an information track and moves the beam back into a position where the intensity of reflected light is optimal for center tracking.
In the case where a tracking servo measures the intensity of light reflected at both edges of an information track, the intensity of reflected light that is optimal for center tracking occurs when the intensity of light reflected at both edges of an information track is the same. The same principle holds true for both one and three beam optical disc storage devices. In the case where a tracking servo measures the intensity of light reflected at one edge of an information track, the intensity of reflected light that is optimal for center tracking is based on some calibrated value. The latter method is less favored due to difficulties associated with calibrating an appropriate centering value.
High Density Mediums
As technology advances, it is desirable to store more information into the medium being recorded to or read from. One manner in which to embed more data in a medium that is comparable in size and compatible with current mediums (i.e., DVDs and CDs) is to create a track that is more tightly spiraled. In this way the disc will have more surface with which to embed the information to be used. This creates problems itself because then the radial distance between each successive track is reduced. This means the laser must be moved radially in a more precise manner. This is difficult and the tracking servo used to accomplish the precise radial movements becomes prohibitively expensive.
Moreover, it would be desirable to cause the laser to traverse the medium quicker. In this way more data can be processed by the system faster, which results in a more satisfying experience for the user. One way to accomplish this using current techniques would be to spin the disc faster. This however creates problems of its own because the inertia of the disc increases as it spins faster, which further exacerbates the problems that already exist in steadying a relatively massive disc as it spins. And to run a tracking servo with a faster spinning disc becomes exponentially more difficult.